1. Technical Field
The invention relates to electronic document delivery. More particularly, the invention relates to a method and apparatus for effecting secure document delivery and format conversion.
2. Decription of the Prior Art
One of the many complexities associated with delivering information between two disparate systems stems from basic incompatibilities between those systems including, for example, differences in capabilities. A printer has a very different set of capabilities than a personal computer, and a commensurate set of data formats which the printer might accept. A personal computer, for example, might be capable of processing a WordPerfect document, a portable document (e.g. Adobe Acrobat or Novell Envoy), or an HTML document. A printer, by contrast, might only be capable of accepting a PCL file or a Postscript file. A fax machine, as with a printer, may only accept a Group 3 compressed black and white raster representation of a document. Thus, various devices have various capabilities in terms of the types of data they may accept.
Similarly, different data types offer different levels of flexibility and function. For example, an Envoy or PDF file can be scaled to any resolution, can support millions of colors, and can include text and fonts. A Group 3 compressed fax image, on the other hand, is limited in resolution, only supports black and white colors, and includes no text or fonts, thereby limiting the ability of a recipient of a Group 3 compressed image to perform any operations, except for rudimentary operations.
The extended flexibility of a more robust data representation, such as a portable document, enables such documents to be converted to less robust representations. By illustration, a portable document might be converted to a Postscript file or even a Group 3 compressed image. One might therefore suggest that a portable document is a high level data representation and a Group 3 compressed image is a low level data representation.
In most cases, if the recipient system is capable of receiving a high level data representation, such representation is the data representation of choice due to the increased capabilities such representation provides. Thus, such representation offers a preferred common format, especially if such representation includes a mechanism that can convert the high level representation to a lower level representation as necessary.
M. Williams, R. Yun, Method and Apparatus For Enhanced Electronic Mail Distribution, U.S. Pat. No. 5,424,724 (Jun. 13, 1995) disclose a method and apparatus for enhanced electronic mail distribution which permits distribution of electronic mail documents to multiple host systems and/or external networks via a single host agent. A host agent reference table is established at selected host agents within a local network. Each host agent reference table includes an identification of selected destination nodes associated with an identified host agent for those nodes. A referral to the host agent reference table is used to determine the appropriate host agent for an electronic document destined for a selected node. No provision is made within this method and apparatus for dynamic data conversion. Thus, documents are delivered with its level of representation unaltered and without regard for processing capability at a destination node.
T. Schultz, A. Gross, B. Pappas. G. Shifrin, L. Mack, Apparatus and Method of Distributing Documents To Remote Terminals With Different Formats, U.S. Pat. No. 4,754,428 (Jun. 28, 1988) and T. Schultz, A. Gross, B. Pappas. G. Shifrin, L. Mack, Electronic Mail, U.S. Pat. No. 4,713,780 (Dec. 15, 1987) disclose a method and apparatus for delivering a document originated at a local site by a source having a printer output that is normally connected to a printer, to one or more remote locations having printers or display devices that may differ from the printer normally connected to the printer output of the document generating source. Printer command signals which are normally provided at the printer output are converted to character and position data which represent the respective characters and their horizontal and vertical positions on each page of the document. The character and position data are transmitted to a remote location and reconverted to a form for driving a printer or other display device to produce a line-for-line conforming copy of the original.
The '428 and '780 patents disclose the use of upstream data conversion, but do not provide downstream data conversion. That is, the '428 and '780 patents disclose a method and apparatus that allows text to be sent to a printer and converted to a printer specific format. However, such method and apparatus lacks the ability to start with a high-level representation of the data, and only convert to a lower level representation if such conversion is determined to be necessary. Thus, such approach is not satisfactory where printer format is not known or established prior to document origination, or where a heterogeneous network, such as the Internet, is used to deliver data.
L. Harkins, K. Hayward, T. Herceg, J. Levine, D. Parsons, Network Having Selectively Accessible Recipient Prioritized Communication Channel Profiles, U.S. Pat. No. 5,513,126 (Apr. 30, 1996) discloses a method for a sender to automatically distribute information to a receiver on a network using devices and communications channels defined in a receiver profile. The receiver profile establishes the properties and mode for receipt of information for receivers on the network and the profile is published in a network repository for all network users or is accessible for selected groups or individuals on the network. The disclosed network does not provide for data conversion, but rather involves sending predetermined data based on the capabilities of the recipient which are communicated through channels. Thus, each recipient must first establish a format before data are exchanged.
M. Bloomfield, Sender-Based Facsimile Store and Forward Facility, I.S. U.S. Pat. No. 5,404,231 (Apr. 4, 1995) discloses a system that provides sender-based store and forward services for delivering facsimile based information. The system is solely concerned with the delivery of facsimile bitmap images, and not with data conversion.
In view of the limitations attendant with the state of the art, it would be advantageous to provide a system in which the ability to descend to a lower level representation is preserved to allow the flexibility to do so at a future point in time, but that also enables a richer set of functions as appropriate. Such as system is described in J. Smith, patent application Ser. No., filed.
One potential shortcoming of the above referenced scheme occurs when secure document delivery is desired. For example, a document may be encrypted with the public key of an intended recipient to prevent unauthorized access to the document. To convert the format of the data within the document, it is first necessary to decrypt the document. Thereafter, the format of the data within the document may be converted and the converted document may then be encrypted. Unfortunately, decrypting the document defeats the purpose of any security that may have been provided to restrict access to the document. That is, the document is readily accessed once it has been decrypted.
J. Chen, J.-S. Wang, Application Level Security System and Method, U.S. Pat. No. 5,602,918 (Feb. 11, 1997) disclose a system and method for establishing secured communications pathways across an open unsecured network by providing secured gateways or a firewall between the Internet and any party which desires protection. The disclosed technique uses a smart card to distribute shared secret keys between a computer which serves as the firewall and a client node on the Internet. The shared private keys establish mutual authentication between the gateway and the smart card. A session or temporary secret key is generated for use in further communications between the gateway and the client node once communications have been established. Further communications are encrypted using the session key. While this approach provides one approach for securing communications across a network, it is not concerned with maintaining security while at the same time allowing document format conversion to occur.
R. Atkinson, Intermediate Network Authentication, U.S. Pat. No. 5,511,122 (Apr. 23, 1996) discloses an internetwork authentication method for verifying a sending host by a receiving host or an intermediate router or gateway. The network address and public key of a receiving host is obtained. The pubic key from the receiving host is used in combination with a private key of the originating host to generate a cryptographic signature. The signature and data are transmitted through a first subnetwork in at least one packet which packet is received at the receiving host. The receiving host uses the private key of the receiving host site and a public key of the originating host to verify the cryptographic signature. While the document discloses a symmetrical form of private key-pubic key cryptography, there is no teaching with regard to secure document format conversion.
A. Aziz, Method and Apparatus for Key-Management Scheme for Use with Intemet Protocols at Site Firewalls, U.S. Pat. No. 5,416,842 (May 16, 1995) discloses a key management scheme for encryption of Internet protocol (IP) data packets between site firewalls. In this scheme, IP packets only from site firewall to site firewall are encrypted. Accordingly, only the firewall servers need to participate in the scheme. When a firewall receives an IP packet from an interior site node intended for a remote firewall, it encrypts the IP packet and sends it encapsulated in another IP packet destined for the remote firewall. The remote firewall decrypts the encapsulated packet and sends it in the clear to the destination node on the interior side of the remote firewall. Accordingly, it is known to encapsulate a document in a secure packet, such that encryption/decryption is performed between two firewalls on the outside of the firewalls. Unfortunately, such scheme does not allow secure conversion of a document format. That is, once the packet is decrypted, the document is no longer secure. Even though the document is now inside the firewall, and thus presumed to be secure, no technique is disclosed that allows the document to be converted to a different format.
It would be advantageous to provide a technique for effecting secure document delivery in any of various document formats.